There is considerable potential utility for printing of information via ink jet streams on targets, e.g., paper. However, for that potential actually to be achieved, it has been required that suitable jet nozzle orifices be designed which with ancillary structure and circuitry can accurately effect sequential drops or droplets of ink appropriately synchronized both temporally and spatially. It has been required that there be both printing via selected drops on a target, e.g. paper, and dispersion of unselected drops away from said target under controllable conditions.
In the prior art of ink jet printing, a mechanical vibration of a jet nozzle has been used to cause hydrodynamic disturbance in the jet stream exiting from the nozzle orifice to cause a separation of the stream into discrete drops. A background reference for ink jet printing with a mechanically vibrated jet stream is an article in IEEE Transactions on Electron Devices, Vol. ED 19, No. 4, April 1972 by Fred J. Kamphoefner entitled "Ink Jet Printing."
Among the prior techniques for establishing mechanically synchronized drop formation in a jet has been the utilization of a piezoelectric driver in order to vibrate the entire jet nozzle structure so that mechanical vibration of the jet stream is amplified as a result of the hydrodynamic instabilities in the jet stream for synchronizing the formation of drops. However, such vibrational technology lacks the appropriate controllability for effecting the jet drop formation and the coordinated jet stream requirements from a plurality of adjacent nozzles. In particular, it is difficult to achieve both uniform control of several jets from an array of nozzle orifices or the individual control of each said jet.
Further, it has been suggested heretofore that an oscillating electric field could synchronize the formation of drops in a jet stream exiting from a jet nozzle orifice. Illustratively, in the background literature, the book Field-Coupled Surface Waves, by J. R. Melcher, MIT Press 1963, at pages 131-135 discusses electrical force perturbation of a jet stream. Further, U.S. Pat. No. 3,586,907 issued June 22, 1971 mentions that an electric signal applied to an electrohydrodynamic plate can generate drops of uniform size in a jet stream at a uniform rate.
It has been determined heretofore that a jet nozzle design with appropriate jet orifice characteristics could be fabricated from a single crystalline region of silicon by chemical etching techniques. Especially suitable technologies for fabricating jet nozzle designs in single crystalline silicon which are useful for the practice of this invention are presented in considerable detail in copending and commonly assigned applications Ser. No. 537,799 filed on Dec. 31, 1974 by E. Bassous and Ser. No. 543,600 filed on the same date as the present application by E. Bassous et al. An article in the Journal of Electrochemical Society, Vol. 114 page 965 et seq., 1965, by R. M. Finne and D. L. Klein, describes chemical etching procedures adequate for fabricating a jet nozzle design useful for the practice of this invention.
It has remained necessary to establish appropriate electrode structures to accomplish electric field drop synchronization for practical ink jet printing purpose. The synchronization effect is electrical in origin and via an electric field perturbs the jet stream electrohydrodynamically. For semantic purpose, the following terminology and the like will be used interchangeably herein: "electrohydrodynamic" or "electric-field" or "electrical" drop synchronization.